Recommendation ITU-R SA.1014-3 (07/2017)

Radiocommunication requirements for manned and unmanned deep space research

SA Series

Space applications and meteorology

ii Rec. ITU-R SA.1014-3

Foreword

The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-

frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of

frequency range on the basis of which Recommendations are adopted.

The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional

Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups.

Policy on Intellectual Property Right (IPR)

ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of

Resolution ITU-R 1. Forms to be used for the submission of patent statements and licensing declarations by patent holders

are available from http://www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent

Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found.

Series of ITU-R Recommendations

(Also available online at http://www.itu.int/publ/R-REC/en)

Series Title

BO Satellite delivery

BR Recording for production, archival and play-out; film for television

BS Broadcasting service (sound)

BT Broadcasting service (television)

F Fixed service

M Mobile, radiodetermination, amateur and related satellite services

P Radiowave propagation

RA Radio astronomy

RS Remote sensing systems

S Fixed-satellite service

SA Space applications and meteorology

SF Frequency sharing and coordination between fixed-satellite and fixed service systems

SM Spectrum management

SNG Satellite news gathering

TF Time signals and frequency standards emissions

V Vocabulary and related subjects

Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1.

Electronic Publication

Geneva, 2017

ITU 2017

All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU.

Rec. ITU-R SA.1014-3 1

RECOMMENDATION ITU-R SA.1014-3

Radiocommunication requirements for manned

and unmanned deep space research

(1994-2006-2011-2017)

Scope

This Recommendation briefly describes some essential characteristics of space research service (deep space)

radiocommunications. These characteristics influence or determine the requirements for selection of candidate

bands, coordination, band sharing and protection from interference.

Keywords

Deep space, radiocommunication, telemetry, telecommand, data rate, earth stations, space stations,

ranging, radio science

Related Recommendations and Reports

Recommendation ITU-R SA.1015, Report ITU-R SA.2167, Report ITU-R SA.2177.

The ITU Radiocommunication Assembly,

considering

a) that radiocommunications between the Earth and stations in deep space have unique

requirements;

b) that these requirements affect the selection of candidate band, band sharing, coordination,

protection from interference and other regulatory and frequency management matters,

recommends

that the requirements and characteristics described in the Annex for deep space radiocommunications

should be taken into account concerning space research service (deep space) and its interaction with

other services.

Annex

Radiocommunication requirements for manned

and unmanned deep space research

1 Introduction

This Annex presents some characteristics of deep space research missions, the functional and

performance requirements for radiocommunications needed to conduct deep space research by means

of spacecraft, and the technical methods and parameters of systems used in connection with such

missions.

2 Rec. ITU-R SA.1014-3

Considerations regarding bandwidth characteristics and requirements are found in Report

ITU-R SA.2177.

2 Radiocommunication requirements

Deep space missions require highly reliable radiocommunications over long periods of time and great

distances. For example, a spacecraft mission to gather scientific information at the planet Neptune

takes eight years and requires radiocommunication over a distance of 4.65 109 km. The need for

high e.i.r.p. and very sensitive receivers at earth stations is a result of the large radiocommunication

distances involved in deep space research.

Continuous usage of space research service (deep space) radiocommunication bands is a consequence

of the several missions now in existence and others being planned. Because many deep space missions

continue for periods of several years, and because there are usually several missions in progress at

the same time, there is a corresponding need for radiocommunication with several spacecraft at any

given time.

In addition, each mission may include more than one spacecraft, so that simultaneous

radiocommunication with several space stations will be necessary. Simultaneous coordinated

radiocommunication between a space station and more than one earth station may also be required.

2.1 Telemetering requirements

Telemetering is used to transmit both maintenance and scientific information from deep space.

Maintenance telemetering information about the condition of the spacecraft must be received

whenever needed to ensure the safety of the spacecraft and success of the mission. This requires a

weather independent radiocommunications link of sufficient capacity. This requirement is a partial

determinant of the frequency bands that are preferred for deep space research (see Report

ITU-R SA.2177).

Science telemetering involves the sending of data that is collected by the on-board scientific

instruments. The required data rate and acceptable error rate may be quite different as a function of

the particular instrument and measurement. Table 1 includes maximum required data transmission

rates for scientific and maintenance telemetering.

TABLE 1

Maximum required bit rates for deep space research

Direction and function

Link characteristic

Weather

independent

Normal High data rate

Earth-to-space

Telecommand (bit/s)

Computer programming (kbit/s)

Audio (kbit/s)

Video (Mbit/s)

1 000

50

45

4

1 000

100

45

12

2 000

200

45

30

Space-to-Earth

Maintenance telemetering (bit/s)

Scientific data (kbit/s)

Audio (kbit/s)

Video (Mbit/s)

500

115

45

0.8

500

500

45

8

2 105

3 105

45

30

Rec. ITU-R SA.1014-3 3

Telemetering link capacity has steadily increased with the development of new equipment and

techniques. This increase can be used in two ways:

– to gather larger amounts of scientific data at a given planet or distance; and

– to permit useful missions to more distant planets.

For a particular telemetering system, the maximum possible data rate is proportional to the inverse

square of the radiocommunication distance. The same link capacity that provides for a data rate of

134 kbit/s from the vicinity of the planet Jupiter (9.3 108 km) would also provide for a data rate of

1.74 Mbit/s from the vicinity of the planet Venus (2.58 108 km). Because higher data rates require

wider transmission bandwidths, the ability to effectively utilize the maximum telemetering capability

depends on the width of allocated bands, and the number of simultaneous mission spacecraft that are

within the earth station beamwidth and are operating in the same band.

An important contribution to telemetering has been the development of coding methods that permit

operation with a lower signal-to-noise ratio. The coded signal requires a wider transmission

bandwidth. The use of coded telemetering at very high data rates may be limited by allocation width.

2.2 Telecommand requirements

Reliability is the principal requirement of a telecommand link. Commands must be received

accurately and when needed. The telecommand link is typically required to have a bit error rate not

greater than 1 10−6. Commands must be received successfully, without regard to spacecraft

orientation, even when the primary high gain antenna may not be pointed towards the Earth. For such

circumstances, reception using a nearly omnidirectional spacecraft antenna is required. Very high

e.i.r.p. is needed at earth stations because of low spacecraft antenna gain, and to provide high

reliability.

With computers on the spacecraft, automatic sequencing and operation of spacecraft systems is

largely predetermined and stored on-board for later execution. For some complicated sequences,

automatic operation is a requirement. Telecommand capability is required for in-flight alteration of

stored instructions, which may be needed to correct for observed variations or malfunctions of

spacecraft behaviour. This is particularly true for missions of long duration, and for those

circumstances where sequencing is dependent on the results of earlier spacecraft events.

For example, the commands for spacecraft trajectory correction are based on tracking measurements

and cannot be predetermined.

The range of required command data rates is given in Table 1.

Reliable telecommand includes the need for reliable maintenance telemetering that is used to verify

that commands are correctly received and loaded into command memory.

2.3 Tracking requirements

Tracking provides information used for spacecraft navigation and for radio science studies.

2.3.1 Navigation

The tracking measurements for navigation include radio-frequency Doppler shift, the round-trip

propagation time of a ranging signal, and the reception of signals suitable for long baseline

interferometry. The measurements must be made with a degree of precision that satisfies navigation

requirements. Measurement accuracy is affected by variations in velocity of propagation, knowledge

of station location, timing precision, and electronic circuit delay in earth and space station equipment.

Table 2 lists a current example of the requirements for navigation accuracy and the associated

measurements.

4 Rec. ITU-R SA.1014-3

TABLE 2

Navigation and tracking requirements

Parameter Value

Navigation accuracy (m) 300 (at Jupiter)

Doppler measurement accuracy (Hz) 0.0005

Range measurement accuracy (m) 0.15

Accuracy of earth station location (m) 1

Ranging (Earth-to-space & space-to-Earth) chip rate*

Weather independent (MChip/s)

Normal (MChip/s)

High rate (MChip/s)

* Transmit or receive pulse rate of a pseudo-random noise (PN) code sequence used for ranging.

2.3.2 Radio science

Spacecraft radiocommunication links can also be important to studies of propagation, relativity,

celestial mechanics and gravity. Amplitude, phase, frequency, polarization and delay measurements

provide the needed information. The opportunity to make these measurements depends upon the

availability of appropriate allocations. Above 1 GHz, transmission delay and Faraday rotation

(charged particle and magnetic field effects) decrease rapidly with increasing frequency, and thus are

best studied with the lower frequencies. The higher frequencies provide relative freedom from these

effects and are more suitable for studies of relativity, gravity and celestial mechanics. For these

studies, calibration of charged particle effects at the lower frequencies is also needed.

Range measurements with an absolute accuracy of 1 to 2 cm are required for this fundamental

scientific work. This accuracy depends upon wideband codes and the simultaneous use of multiple

frequencies for charged-particle calibration.

2.4 Special requirements for manned deep space missions

The functional requirements for such missions will be similar in kind to those for unmanned missions.

The presence of human occupants in spacecraft will, however, place additional requirements for

reliability on the telemetering, telecommand and tracking functions. Given the necessary level of

reliability, the significant difference between manned and unmanned missions will be the use of audio

and video links for both Earth-to-space and space-to-Earth radiocommunication. Data rates for these

functions are shown in Table 1.

From a radiocommunication standpoint, the effect of these additional functions will be a required

expansion of transmission bandwidth in order to accommodate the video signals. Given the necessary

link reliability and performance needed to support the required data transfer rates,

radiocommunications for manned and unmanned deep space research are similar.

Rec. ITU-R SA.1014-3 5

3 Technical characteristics

3.1 Locations and characteristics of space research service (deep space) earth stations

Table 3 gives the locations of earth stations with the capability of operating within bands allocated

for deep space research.

TABLE 3

Location of space research service (deep space) earth stations

Administration Location Latitude Longitude

China Kashi 38° 55' N 75° 52' E

Jiamusi 46° 28' N 130° 26' E

European Space Agency Cebreros (Spain) 40° 27' N 4° 22' W

Malargüe (Argentina) 35° 46' S 69° 22' W

New Norcia (Australia) 31° 20' S 116° 11' E

Germany Weilheim 47° 53' N 11° 04' E

Ukraine Evpatoriya 45° 11' N 33° 11' E

Russia Medvezhi ozera 55° 52' N 37° 57' E

Ussuriisk 44° 01' N 131° 45' E

Japan Usuda, Nagano

Uchinoura

36° 08' N

31° 15' N

138° 22' E

131° 04' E

United States Canberra (Australia) 35° 28' S 148° 59' E

Goldstone, California (United States) 35° 22' N 115° 51' W

Madrid (Spain) 40° 26' N 04° 17' W

India Byalalu 12° 54' N 77° 22' E

At each of these locations there are one or more antennas, receivers and transmitters that can be

utilized for space research service (deep space) links in one or more of the allocated bands. The

principal parameters that characterize the maximum performance of one or more of these stations are

listed in Table 4. Although these characteristics do not apply to all stations, it is nevertheless essential

that band allocations and criteria for protection from interference be based on the maximum

performance available. This is required in order to provide for international operation and protection

of space research service (deep space) missions.

6 Rec. ITU-R SA.1014-3

TABLE 4

Characteristics of space research service (deep space) earth stations with 70 m antennas

Frequency

(GHz)

Antenna

gain

(dBi)

Antenna

beamwidt

h

(degrees)

Transmitte

r

power

(dBW)

e.i.r.p.

(dBW)

Receiving

system

noise

temperatur

e

(K)

Receiving

system noise

power

spectral

density

(dB(W/Hz))

2.110-2.120

Earth-to-space

62 0.14 50

56(1)

112

118(1)

– –

2.290-2.300

Space-to-Earth

63 0.13 – – 25(2)

21(3)

–214(2)

–215(3)

7.145-7.190

Earth-to-space

72 0.04 43 115 – –

8.400-8.450

Space-to-Earth

74 0.03 – – 37(2)

27(3)

–213(2)

–214(3)

31.8-32.3

Space-to-Earth

83.6(4) 0.01(4) – – 83(2) (4)

61(3) (4)

–209(2) (4)

–211(3) (4)

34.2-34.7

Earth-to-space

84(4) 0.01(4) 30(4) 114(4) – –

(1) 56 dBW transmitter power used only during spacecraft emergencies. (2) Clear weather, 30° elevation angle, duplex mode for simultaneous transmission and reception. (3) Clear weather, 30° elevation angle, receive only. (4) Estimate.

The receiving performance of space research service (deep space) earth stations is usually specified

in terms of the ratio of signal energy per bit-to-noise spectral density required to give a particular bit

error rate. Another way to show the high performance and sensitivity of these stations is to express

the ratio of antenna gain-to-noise temperature. This quotient, commonly referred to as G/T, is

approximately 50 dB/(K) at 2.3 GHz, and 59.5 dB/(K) at 8.4 GHz. These values may be compared

with the lower and typical 41 dB/(K) of some fixed satellite earth stations.

3.2 Space stations

Spacecraft size and weight are limited by the payload capability of the launch vehicle. The power of

the space station transmitter and the size of the antenna are limited in comparison with those

parameters at earth stations. The noise temperature of the receiver is higher because an uncooled

preamplifier is generally used.

The space station has a combined receiver-transmitter, called a transponder, which operates in one of

two modes. In the turn-around (also called two-way) mode, the carrier signal received from an earth

station is used to control the oscillator in a phase-locked signal loop. The frequency of this oscillator

is then used to control the transmitter frequency of the transponder according to a fixed ratio. In the

one-way mode, the spacecraft transmitter frequency is controlled by a crystal oscillator.

In the two-way mode, the spacecraft transmitted frequency and phase is controlled very precisely

because of the extreme accuracy and precision of the signal received from an earth station.

Table 5 lists major characteristics that are typical of space stations designed for deep space research.

Rec. ITU-R SA.1014-3 7

TABLE 5

Characteristics typical of space stations for deep space research

Earth-to-

space

frequency

(GHz)

Antenna

diameter

(m)

Antenna gain

(dBi)

Antenna

beamwidth

(degrees)

Receiver noise

temperature

(K)

Receiver noise

spectral power

density

(dB(W/Hz))

2.110-2.120 3.7 36 2.6 200 −206

7.145-7.190 3.7 48 0.64 330 −203

34.2-34.7 3.7 61 0.14 2 000 −196

Space-to-

Earth

frequency

(GHz)

Antenna

diameter

(m)

Antenna gain

(dBi)

Antenna

beamwidth

(degrees)

Transmitter

power

(dBW)

e.i.r.p.

(dBW)

2.290-2.300 3.7 37 2.3 13 50

8.400-8.450 3.7 48 0.64 13 61

31.8-32.3 3.7 59.5 0.17 13 72.5

Because of the limited e.i.r.p. of space stations, the earth station must have the most sensitive receiver

possible. Receivers with lower sensitivity may be used in space stations as a result of the very high

e.i.r.p. of the earth station. Data rate requirements and considerations of size, weight, cost, complexity

and reliability determines the receiver noise temperature needed for a particular spacecraft.

The power of the space station transmitter is limited primarily by the electrical power that can be

supplied by the spacecraft.

4 Methods deep space radiocommunication

Telemetering and telecommand functions for deep space radiocommunications are typically

accomplished by transmission of phase modulated carriers. Doppler tracking is done by phase

coherent detection of the received carrier. By adding a ranging signal to the modulation, the ranging

function may be performed.

4.1 Carrier tracking and Doppler measurement

As received on Earth, the frequency of a signal transmitted by the spacecraft is modified by the

Doppler effect. The means to measure the Doppler shift, and hence the velocity of the spacecraft with

respect to the earth station, is provided by carrier phase tracking. Earth and space station receivers

track the carrier signal with a phase-locked loop or a Costas loop. In the two-way transponder mode,

the frequency and phase in the space station phase-locked loop are used to develop one or more space-

to-Earth frequencies. This provides signals to the earth station that are correlated with the Earth-to-

space frequency, enabling precise Doppler measurements to be made.

In the one-way mode, the space-to-Earth frequencies are derived from the oscillator in the

transponder, and the Doppler measurement is based on a priori knowledge of the oscillator frequency.

8 Rec. ITU-R SA.1014-3

4.2 Modulation and demodulation

The radio links use phase modulation of the radio-frequency carrier. The baseband digital data signal

is used to modulate a subcarrier, which in turn phase modulates the radio-frequency carrier. A square

wave sub-carrier is typically used for telemetering; for telecommand the sub-carrier is often

sinusoidal. The modulation index is adjusted to provide a desired ratio of residual carrier power to

data sideband power. This ratio is selected to provide optimum carrier tracking and data detection in

the receiver.

RF carrier and data sub-carrier demodulation is accomplished by phase-locked loops (PLLs). Data

detection generally uses correlation and matched filter techniques.

Video and audio links for manned missions may use other modulation and demodulation techniques.

Typically, bandwidth-efficient (offset) QPSK and GMSK modulation and demodulation are used in

these cases with carrier tracking accomplished via Costas loops instead of PLLs.

4.3 Coding

In a digital telecommunication link, error probability can be reduced if the information bandwidth is

increased. Coding accomplishes this increase by translating each data bit into a larger number of code

symbols in a particular way. Some examples of coding types are block and convolutional codes. After

transmission, the original data are recovered by a decoding process that is matched to the code type.

The performance advantage of coded transmission is related to the wider bandwidth, and can vary

from to 3.8 dB (convolutional coding, bit error ratio of 1 10−3) to more than 9 dB (rate 1/6 turbo

coding).

4.4 Multiplexing

Science and maintenance telemetering may be combined into a single digital data stream by time

division multiplexing; or may be on separate sub-carriers that are added to provide a composite

modulating signal. A ranging signal may also be added in combination with telemetering or

telecommand. The amplitude of the different data signals is adjusted to properly divide the transmitter

power between the carrier and the information sidebands.

4.5 Ranging

Ranging is performed from an earth station using the space station transponder in the two-way mode.

Ranging modulation on the Earth-to-space signal is recovered in the transponder and used to modulate

the space-to-Earth carrier. At the earth station, comparison of the transmitted and received ranging

codes yields a transmission delay measurement proportional to distance.

A fundamental limitation to ranging precision is the ability to measure time correlation between the

transmitted and received codes. The system currently in use employs a highest code frequency of

2.062 MHz. The code period is 0.485 s and resolution to 1 ns is readily achieved, assuming sufficient

signal-to-noise ratio. This resolution is equivalent to 30 cm in a two-way path length, 15 cm in range.

This meets the current navigation accuracy requirements of Table 2.

For the 1 cm accuracy needed for radio science experiments (see § 2.3.2) a code frequency of at least

30 MHz is required. Current SRS deep space pseudo-noise (PN) ranging systems use a maximum

chip rate of 24 MChip/s.

4.6 Antenna gain and pointing

For the parabolic antennas typically used in space research, the maximum gain is limited by the

accuracy with which the surface approaches a true parabola. This latter limitation places a bound on

the maximum frequency that may be effectively used with a particular antenna.

Rec. ITU-R SA.1014-3 9

One factor in surface accuracy, common to both earth and space station antennas, is manufacturing

precision. For earth station antennas, additional surface deformation is caused by wind and thermal

effects. As elevation angle is varied, gravity introduces distortion of the surface, depending on the

stiffness of the supporting structure.

For space station antennas, size is limited by permissible mass, by the space available in the launch

vehicle, and by the state of the art in the construction of unfurlable antennas. Thermal effects cause

distortion in space station antenna’s surfaces.

The maximum usable gain of antennas is limited by the ability to point them accurately. The

beamwidth must be adequate to allow for the angular uncertainty in pointing. All the factors that

cause distortion of the reflector surface also affect pointing accuracy. The accuracy of the spacecraft

attitude control system (often governed by the amount of propellant which can be carried) is a factor

in space station antenna pointing.

The precision with which the location of the earth and space stations are known with respect to each

other affects the minimum usable beamwidth and the maximum usable gain.

Table 6 shows typical limits on antenna performance.

TABLE 6

Current limitations on accuracy and maximum antenna gain

Space station antennas Earth station antennas

Limiting

parameter

Typical

maximum

value of

parameter

Maximum gain Typical

maximum

value of

parameter

Maximum gain

Accuracy of dish

surface

0.24 mm r.m.s.,

3.7 m dish

61 dBi(1) at 34

GHz

0.53 mm r.m.s.,

70 m dish

84 dBi(1) at

34 GHz

Pointing accuracy 0.15° (3) 56 dBi(2) 0.005° (3) 82.5 dBi(2)

(1) Gain at other frequencies will be lower. (2) Gain of antenna with half power beamwidth equal to 2 times pointing accuracy. The beamwidth of an

antenna with higher gain will be too narrow with respect to pointing accuracy.

4.7 Additional radionavigation techniques

Doppler and ranging measurements provide the basic tracking information needed for navigation.

Additional techniques have been developed to enhance navigation accuracy.

4.7.1 Calibration of the velocity of propagation as affected by charged particles

Range and Doppler measurements are influenced by variations in the velocity of radio-wave

propagation caused by free electrons along the transmission path. The electrons exist in varying

densities in space and in planetary atmospheres, and are particularly dense near the Sun. Unless

accounted for, these variations in propagation velocity can introduce errors in navigation calculations.

The charged particles cause an increase in phase velocity and a decrease in group velocity. By

comparing range change with integrated Doppler over a period of time, the charged particle effect

may be determined.

The effect on propagation velocity is inversely proportional to the square of the radio frequency. This

frequency dependency may be used for additional calibration accuracy. Turnaround ranging and

10 Rec. ITU-R SA.1014-3

Doppler tracking can be performed with simultaneous space-to-Earth signals in two or more separate

bands. The charged particle effects in the separate bands are different in magnitude, and this

difference is used to improve the calibration.

The effect of charged particles on phase and group velocity as well as on range measurement is given

in Report ITU-R SA.2177.

4.7.2 Very long baseline interferometry (VLBI)

Accuracy of spacecraft navigation depends upon the precise knowledge of earth station location with

respect to the navigation coordinate system. A 3 m error in the assumed station location can result in

a 700 km error in the calculated position of a spacecraft at Saturn distance. VLBI provides a means

of improving the estimate of station location by using a celestial radio source (quasar) as a signal

source at an essentially unchanging point on the celestial sphere. It is possible to record the quasar

signals in such a way as to determine, with great accuracy, the difference in time of reception at two

widely separated stations. Using several of these measurements the station locations can be

determined to a relative accuracy of 10 cm. Frequencies near 2, 8 and 32 GHz are used for VLBI at

the present time.

The VLBI technique is also used to measure directly the spacecraft declination angle. Two accurately

located earth stations separated by a large north/south distance, measure the range to the spacecraft.

The declination can then be calculated with great precision.

A third application of the VLBI method, called DDOR, can be used to improve the accuracy of

measurement of spacecraft angular position. Two or more earth stations alternately observe a

spacecraft signal and a quasar signal. By knowing time, station location and the effect of Earth

rotation on the received signals, the angular position of the spacecraft can be determined with respect

to the celestial references. When fully developed the techniques will provide a 10-fold improvement

over the current accuracy of 0.002 arc second (equivalent to 10 nrad). The improved accuracy will

permit more precise navigation and, as a consequence, a more efficient planetary orbit insertion.

5 Performance analysis and design margins

Table 7 shows a link budget used for performance analysis. The example given is for high rate

telemetering from Jupiter. Similar analysis for telecommand and ranging is performed. The earth and

space station characteristics shown earlier are used as the basis for calculating a performance margin

for each radiocommunication function.

Rec. ITU-R SA.1014-3 11

TABLE 7

Performance budget, spacecraft-to-Earth from Jupiter

Mission: Voyager Jupiter/Saturn 1977

Mode: Telemetering, 115.2 kbit/s, coded, 8.45 GHz carrier

Transmitter parameters

RF power (21 W) (dBW)

Circuit loss (dB)

Antenna gain (3.7 m) (dBi)

Pointing loss (dB)

0013.2

00–0.2

0048.1

00–0.2

Path parameters

Free space loss between isotropic antennas (dB)

(8.45 GHz, 9.3 108 km)

–290.4

Receiver parameters

Antenna gain (64 m, 30° elevation angle) (dBi)

Pointing loss (dB)

Weather attenuation (dB)

System noise power spectral density (22.6 K) (dB(W/Hz))

0072.0

00–0.3

00–0.1

–215.1

Total power summary

Link loss (dB)

Received power P(T) (dBW)

–171.1

–157.9

Carrier tracking performance (two-way)

Carrier power/total power (dB)

Received carrier power (dBW)

Carrier threshold noise bandwidth (B 10 Hz) (10 log B)

Noise power (dBW)

Threshold signal/noise (dB)

Threshold carrier power (dBW)

Performance margin (dB)

0–15.4

–173.3

0010.0

–205.1

000020

–185.1

0011.8

Data detection performance

Data power/total power (dB)

Data reception and detection losses (dB)

Received data power (dBW)

Noise bandwidth (effective noise bandwidth for matched filter detection of

115.2 kbit/s data) (dB)

Noise power (dBW)

Threshold signal/noise (5 10–3 bit error rate) (dB)

Threshold data power (dBW)

Performance margin (dB)

00–0.3

00–0.5

–158.7

0050.6

–164.5

0002.3

–162.2

0003.5

12 Rec. ITU-R SA.1014-3

A most important point in the design of deep space missions is that the telemetering performance

margin is quite small (3.5 dB in the example given). This small margin is a consequence of the need

to obtain maximum scientific value from each spacecraft. To design with a 10 dB larger margin of

safety would reduce the quantity of telemetered data by a factor of 10. The risk of using a system

with small performance margin is its susceptibility to harmful interference, and for bands above

2 GHz, decreased reliability caused by weather effects.